This invention generally relates to printer apparatus and methods and more particularly relates to an ink jet printer capable of increasing spatial resolution of a plurality of marks to be printed thereby and method of assembling the printer.
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In one type of ink jet printer, ink is disposed in a plurality of ink chambers formed in a print head. An orifice in communication with the chamber opens onto a receiver medium which receives ink droplets ejected from the orifice. The means of ejection may, for example, be a piezoelectric crystal coupled to the chamber and deformable when subjected to an electric pulse. When the crystal deforms, a pressure wave is produced in the ink in the chamber, which pressure wave ejects one or more ink droplets through the orifice. Other types of ink jet printers include heaters for lowering surface tension of an ink meniscus residing in the orifice, so that an ink droplet is released from the orifice when the surface tension is sufficiently lowered.
Moreover, in ink jet printing it is common to use a technique referred to as "interlace printing" in order to increase printed resolution. With regard to interlace printing, a print head having a plurality of printing elements is swept in a reciprocating motion across a receiver. After one or more such reciprocating passes, the print head is then moved in uniform increments of distance with respect to the receiver in a direction perpendicular to the reciprocating motion in order to achieve the afore-mentioned interlaced printing.
Such an interlace ink jet printer is disclosed in U.S. Pat. No. 4,069,486 titled "Single Array Ink Jet printer" issued Jan. 17, 1978, in the name of S. J. Fox. This patent teaches printing an interlace pattern with a single array of ink jet nozzles. According to this patent, number of individual print elements N, print element spacing p, printed pel spacing D, and printhead-receiver displacement distance delta-x must bear a predetermined relationship to each other, in order for interlaced printing to occur, without doubly printed lines or spaces. Namely, if the print element spacing p is equal to kD, then the displacement delta-x must be chosen equal to ND. Furthermore, k must be an integer chosen such that, when k is divided by N, the result is an irreducible fraction. Thus, there is a required relationship between N, D and delta-x.
Multiple resolution ink jet printers are known. A multiple resolution ink jet printer is disclosed in U.S. Pat. No. 4,401,991 titled "Variable Resolution, Single Array, Interlace Ink Jet Printer" issued Aug. 30, 1983, in the name of Van C. Martin. This patent discloses a multiple-resolution, interlace, ink jet printer that uses a single array with multiple nozzles of constant pitch. In one embodiment of the Martin device, the single array achieves multiple-resolution printing by disabling some of the nozzles while adjusting translation motion of the array, so that dot rows can be printed closer together in order to increase spatial resolution. In this manner, the fixed pitch of the nozzles is not an impediment to increasing spatial resolution of the image to be printed. Thus, the Martin technique represents an improvement over the Fox technique in that pel spacings D can be varied using the Martin technique. However, it appears the Martin technique of increasing spatial resolution is not cost-effective because, at least in one embodiment of the Martin device, some of the nozzles are initially disabled and therefore do not print. Manufacture of unused nozzles increases material and fabrication costs of the printer and is thus wasteful. It would therefore be desirable to provide a printing device and technique that increases spatial resolution while using all available nozzles.
A disadvantage of the prior art techniques recited hereinabove is that the relative displacement of the printhead and the receiver must be precise, and that the relative motion be large enough to cover the length of the print. If the motion is not precise, then the interlaced sets of lines may be improperly spaced, leading to unwanted density variations in the printed image. Unwanted density variations can be camouflaged by multiple passes of the printhead. However, multiple passes of the printhead increases printing time. It is difficult to inexpensively and precisely translate the printhead over the required distance; thus, typically the receiver or paper is translated relative to the printhead. However, this results in the need for two translation systems in the printer, one for the printhead and one for the paper, which adds to manufacturing costs.
A further disadvantage of the prior art recited hereinabove is that the relative displacement of the printhead and the receiver should be accurate, and that this relative motion be large enough to cover the length of the print. If the motion is not accurate, then it may not be possible to provide controllable minimal displacements delta-x small enough to achieve high-resolution, high-quality printing.
Consequently, in order to avoid the disadvantages recited hereinabove, it is desirable to provide an ink jet printing technique wherein there is no required relationship between N, D, and delta-x; wherein the printhead-receiver motion may be other than uniform; wherein required relative motions between printhead and receiver may be provided with increased precision and accuracy over the required range; and wherein one of the two motion translation systems required of the prior art is unnecessary.
Therefore, there is a need to provide a suitable ink jet printer capable of increasing spatial resolution of a plurality of marks to be printed thereby and method of assembling the printer.